Patent GB-1389284-A (GB)
Title: Vessel inspection device
IPC: B25J18/02
Filed: 1972-04-20
Abstract: 1389284 Winches; manipulators PROGRAMMED & REMOTE SYSTEMS CORP 20 April 1972 [22 April 1971] 18342/72 Headings B8B and B8H [Also in Division H4] Apparatus for inspecting the interior surface of a nuclear reactor pressure vessel comprises a telescopic tube assembly 24 extensible along a vertical axis coincident with that of the vessel; a transverse boom assembly 51 mounted at the lower end of the tube assembly 24 the boom assembly being displaceable angularly about the vertical axis; an inspection unit mounted on the boom assembly 51; and position detection and indication means for indicating the position of the boom assembly along the vertical axis and for indicating the angular position of the boom assembly about the vertical axis. The telescopic, tube assembly can be extended and retracted by a winch 31. A tripod mounting arrangement for centring the apparatus by engagement of the tripod legs 20 with respective studs 17 extending vertically from the vessel comprises legs two of which embody pivoted-jaw clamping devices (Figs. 3-5, not shown) which are operative to centre the tube assembly 24 accurately relative to the vessel. The transverse boom assembly 51 comprises telescopic tubes which are arranged to be extended and retracted by a double-acting ram (Fig. 7, not shown). Alternatively, or in addition, the boom comprises a manipulator 81 which can be used to mount an inspection unit or to position various other components mounted on the boom. Electrical encoders, such as are described with reference to the boom assembly (Fig. 11, not shown) are provided to indicate the axial extension of tube assembly 24 and boom assembly 51 and angular position of the boom assembly about the axis of the tube assembly 24. Pivoting movements of the manipulator may also be encoded (Fig. 8, not shown). Since the vessel to be inspected may contain water, components at the lower end of the tube assembly 24 receive compressed air to maintain a pressure differential which acts to exclude water from them. The differential is maintained irrespective of depth of immersion by a relay which senses the water pressure (Fig. 12, not shown).  The inspection unit may comprise an ultrasonic device or a television camera and lights. The winch 31 comprises a pair of drums 93, 118. A motor 104 drives bevel gearing 105, 106 the latter being fast on shaft 102. Winch drum 93 is rotatable on the shaft 102 but is normally driven therewith by engagement of a pin 107 projecting from gear 106 against a shoulder defined between ramp surfaces on the hub of drum 93. At the other end of drum 93 is a gear 110 followed, in the axial direction by a friction disc 111, ratchet wheel 112, another friction disc 111 and finally a hub 113 on the shaft 102. A pawl 115 permits rotation of the ratchet wheel in one direction only. A cable 92 wound on the drum passes to a load pulley 90 and then returns to a slidable, spring urged anchor member 94. With the cable under normal tension, the head of member 94 is retained in a lower position; should the tension be relaxed, the head is raised by the spring 97 to trip a switch 98 to turn off the winch motor 104 and actuate a brake 123. The latter is rotated by drive transmitted from drum 93 via gear 110, intermeshing gear 117 on drum 118 and bevel gearing 121, 122. A rotary limit switch 126 is driven from gear 117 to control the maximum extension of the cable 92 or cable 119 wound on the drum 118. The cable 119 also is connected to an anchor member 94A which can operate a motor and brake control switch 98A. The provision of two cables provides redundancy in the winch operation and is a safety provision. An electrical encoder 130 indicates the amount of pay-out of the cables. The provision of the ratchet and friction discs is a "fail-safe"; if, for any reason, the loadpulleys 90, 91 start to fall and the brake 123 does not operate, the drums 93, 118 are driven in reverse by the unwinding of the cables. As drum 93 runs in reverse, the driving pin 107 runs up the ram surfaces and hence the drum is urged towards the limb 113. Pawl 115 prevents rotation of the ratchet wheel 112 and the tightening of the friction discs 111 against the wheel 112 due to the axial movement of the drum 93 brakes the latter.